Quantifying and modelling the contribution of streams that recharge the Querença-Silves aquifer in the south of Portugal

Abstract

Abstract. The water balance of the mesocenozoic aquifers of the Algarve, in the south of Portugal has traditionally been estimated considering only direct ("autogenic") recharge from rainfall occurring in the area of the aquifers. Little importance has been attributed to so-called allogenic recharge, originating from streambed infiltration from runoff generated outside the aquifers, particularly in the Palaeozoic rocks to the north where runoff is high. The Querença-Silves (QS) aquifer is the most important aquifer of the region both for irrigation and public water supply. Several important and sensitive surface/groundwater ecotones and associated groundwater dependent ecosystems exist at the springs of the natural discharge areas of the aquifer system. A numerical flow model has been in constant development over the last few years and currently is able to reproduce the aquifer's responses to estimated direct recharge and abstraction for the years 2001-2010. However, recharge calculations for the model do not take into account allogenic recharge infiltration along influent reaches of streams. The quantification of allogenic recharge may further improve the assessment of water availability and exploitation risks. In this paper an attempt is made to quantify the average annual contribution of allogenic recharge to the QS aquifer, based on monitoring data of the principal water courses that cross the aquifer system. Significant uncertainties related to surface runoff generated within the aquifer area, as well as areal recharge were identified and the consequences for the optimization of spatial distribution of transmissivity in the groundwater flow model are also addressed.

Climatic and geologic controls on the piezometry of the Querença-Silves karst aquifer, Algarve (Portugal)

“…All these observations are consistent with the regional flow pattern model developed for the QS aquifer (Monteiro et al 2006;Stigter et al 2010;Hugman et al 2012;. The spatial distribution of the porous-karst media equivalent transmissivity in the aquifer has been obtained in previous studies using inverse calibration of finite element model predictions against piezometric and discharge data , and considering both autogenic and allogenic recharge (Salvador et al 2012). In the western sector, the models show a regular distribution of high transmissivity values, indicative of a well-developed karst conduit network that supports high rates of water flow.…”

Modeling the spatial and temporal distribution of coastal groundwater discharge for different water use scenarios under epistemic uncertainty: case study in South Portugal

“…Apart from issues of adequate groundwater quantity and quality for human needs, there is a need to determine criteria for sustainability which take into account other users such as GDE. Various GDEs have been identified in the Algarve, mostly related to springs and streams connected to groundwater bodies (Reis 2007;Salvador et al 2012;Fernandes 2013), but little attention has been given to the dependence of marine ecosystems on fresh groundwater discharge.…”

“…Several efforts during the past few years have begun to analyze the factors that influence sustainable groundwater use in the region Salvador et al 2012;Stigter et al 2013a;Hugman et al 2013;Stigter et al 2014). Apart from issues of adequate groundwater quantity and quality for human needs, there is a need to determine criteria for sustainability which take into account other users such as GDE.…”

Preface "2nd International Conference on Ecohydrology and Climate Change"

“…The results obtained are useful, providing reservoir response at different time scales while acknowledging the associated level of uncertainty. Salvador et al (2012) discussed the importance of allogenic recharge in aquifers, the attempt to quantify the response of the Querença-Silves aquifer to allogenic recharge, for further inclusion in a groundwater flow numerical model that already reproduces the aquifer response to autogenic recharge and abstraction in the period 2001-2010.…”